1. Introduction Active Galactic Nuclei
Jets

2. Radio Galaxies and radio-loud Quasars
Radio galaxies & radio-loud quasars:
the most powerful radio sources
(Usually) extended (or very extended!) radio emission
with common characteristics (core-jets-lobes)‏
Typically hosted by an elliptical (early-type) galaxy
Amazing discovery when they were identified with
extragalactic, i.e. far away, objects
Unexpectedly high amount of energy involved!
The radio contribute only to a minor
fraction of the energy actually released by these AGNs.
(ratio between radio and optical luminosity ~10-4)‏
However, the kinetic power in jets can be a significant fraction of the accretion energy

3. Why study radio-loud AGN?
They show most of the phenomena typical of AGNs
(e.g. optical lines, X-ray emission etc.)
very interesting objects in (almost) all wavebands
In addition they have
spectacular radio morphologies
But they are quite rare!

4. Some Radio surveys
Start: 3CR (Cambridge Telescope)  328 sources with  > - 5o
flux above MHz
(1 Jy= W m-2 Hz-1)‏ 4C
2Jy
178 MHz
Cambridge (+5,6,7C)‏
PKS
~3Jy
408 MHz
Parkes
Molonglo B2
0.25
Bologna (+B3)‏
NRAO
0.8Jy
1.4-5GHz
0.7Jy
2.7 GHz
NVSS
2.5 mJy (45” res.)‏
1.4 GHz
NRAO VLA Sky Survey
FIRST
1mJy (~5” res)‏
Faint Images Radio Sky at Twenty centimeters
WENSS
300 MHz
WSRT

5. A prototypical radio galaxy
Lobes
Core
Hot-spots
Jets
Any size: from pc to Mpc
First order similar radio morphology
(but differences depending on radio power,
optical luminosity & orientation)‏
Typical radio power 1023 to 1028 W/Hz

6. Note the scales on both axis!
Radio Spectrum
S
steep: <-0.5
flat: >-0.5
inverted: >0
Note the scales on both axis!
Steep spectrum with breaks
flat/inverted/peaked & variable spectrum
Carilli et al. (1999)

7. Radio-Dichotomy
Optically bight quasars come in two flavors: radio-loud and radio-quiet
This is seen in a homogenous optically selected sample (e.g. PG/BQS quasar sample).
Normalizing the radio emission (jet) by the optical luminosity (disk): only 10% of quasars are radio-loud.
In both groups radio comes from jets! Why the difference in efficiency?
It is not clear whether that persists also at lower masses and accretion rates…
Only Steep-Spectrum Quasars!
Ellipticals + Spirals
Ellipticals
R=radio/optical flux
Kellermann et al. (1989) Falcke, Sherwood, Patnaik (1996)

8. Jet-Disk Symbiosis (looking at radio core only!)
4/17/2017
Jet-Disk Symbiosis (looking at radio core only!)
Jet power scales with accretion disk power Qjet = qj/l · Ldisk  Sradio  L17/12
Model applicable to
quasars
LLAGN
X-ray binaries
Radio Core Luminosity
Seyferts
Accretion disk luminosity
Falcke et al. ( )

9. 4/17/2017
Jets exist on all scales and also in “radio quiet” AGN: Seyfert Galaxies

10. Radio Structures in Seyferts

11. VLA Observations of RQQs (Radio Quiet Quasars)
Leipski, C.; Falcke, H.; Bennert, N.; Hüttemeister, S. (2006)

12. Jets exist on all scales
4/17/2017
Jets exist on all scales
X-ray binaries
Low-Luminosity AGN
Mirabel & Rodriguez (1994)
VLBI: Falcke, Nagar, Wilson et al. (2000)

13. Jets Not well understood Emitted from axis of rotation
Acceleration through magnetic fields
Acceleration of charged particles from strong magnetic fields and radiation pressure
Synchrotron Radiation
Produces radiation at all wavelengths especially at Radio wavelengths
Possible source of Ultra high energy cosmic rays and neutrinos

14. Jets
Often the radio emission is more symmetric on the large scale and asymmetric on the small scale
The core is defined based on
the spectral index: flat ( ~ 0)‏
[to find which component is
the radio core is not always easy:
free-free absorption can
complicate the story!]
core

15. Jet in M87
Discovery of AGN jet (Active Galactic Nucleus) in M87 (Curtis 1918)
“...curious straight ray...”
Is: optical synchrotron radiation from relativistic plasma jet ejected from black hole
Hubble shows super-luminal motion v~6c
HST: Biretta et al. (1999)

16. Black Hole powered jet in M87
4/17/2017
Black Hole powered jet in M87
Reid et al. (1999, Space VLBI)

17. Jets Collimation Going very close to the BH to see how the collimation
of the jet works.
rapid broadening of the jet
opening angle as the core is
approached on scale below
1 mas (0.1 pc).
43 GHz
VLBI
~ 1 mas = pc
M 87
The jet does not seem to reach a complete collimation until a distance
of many tens of Schwarzschild radii (escape velocity = c)‏
Jet emanating from the accretion disk, not yet collimated

18. Monitoring of the quasar 3C120 with VLBI
4/17/2017
Monitoring of the quasar 3C120 with VLBI

19. Superluminal motions
Read old jet lecture on superluminal motion and beaming!
These projection effects explain:
the apparent superluminal motion
the asymmetry between the two jets, also the flux of the approaching and receding components are affected by projection (Doppler Boosting)‏
These are among the methods used to find out the orientation of a source

20. Jet to Counter Jet Ratios: boosting & de-boosting
The jet to counter jet ratio of the inner jet can be modeled by a relativistic, decelerating jet with a fast spine and a slower shear layer (Laing & Bridle 2002).
The observed jet/counter-jet brightness ratio (sided-
ness) at a resolution of 0.75 arcsec, from the 8.4-GHz observations. This was constructed by dividing the image by a copy of itself rotated through 180 degree and is in the sense main jet/counter-jet.

21. 3C31: Jet to Counter Jet Ratios

22. BL Lacs – looking down the jet
4/17/2017
BL Lacs – looking down the jet
Read old jet lecture on superluminal motion and beaming!
Synchrotron from jet
Reprocessed radiation from jet
BL Lacs are thought to be beamed FRI radio galaxies ponting at us.
Relativistic beaming will lead to an enhancement of the core emission by a huge factor (103)
In BL Lacs the emission is completely dominated by the innermost jet.
The spectrum is “flat” in S and rising linearly with  in a S plot.
There is no evidence for a disk spectrum (probably because FRIs have a radiatively inefficent disk/ADAF).
The spectrum resembles a „camel‘s back“.
Radio - optical: synchrotron emission from jet
X-ray – TeV: inverse Compton or hadronic cascades (e-, p-)
Z~100 Rg  S  
Fossati et al. (1998)

23. Jet Formation
All relativistic cosmic jet sources may be connected by a common basic mechanism
A promising model for that is magnetohydrodynamic acceleration by rotating, twisted magnetic fields
“Spin Paradigm” can explain qualitatively a number of statistical properties of AGN
Geometrically thick accretion flows are more efficient at launching jets
In Microquasars this principle may explain the correlation between the production of a jet and the presence of a hot, geometrically thick accretion flow
This also may be testable in some Seyfert AGN as well
Slow acceleration and collimation of these jets is probably the norm
There is some evidence for this in AGN jets
Highly relativistic jet flows may be produced by strong, straight magnetic fields
All galactic cosmic jet sources, including supernovae and gamma-ray bursts, may be connected by a common origin as well: different outcomes of the last stage of evolution in a massive star

24. Basic Principles of Magnetohydrodynamic Jet Production
Basic MHD mechanism:
Blandford (1976); Lovelace (1976)
Acceleration by rotating black holes (Blandford & Znajek [1977])
Acceleration by rotating [thin] accretion disks (Blandford & Payne [1982])
First numerical simulations: Uchida & Shibata (1985)
Key ingredients in their “Sweeping Pinch” mechanism
Thick accretion disk or torus
Keplerian differential rotation (  R-3/2)
Initial strong vertical magnetic field
(strong enough to slow disk rotation)
J  B force splits up into magnetic pressure and tension: - (B2 / 8) + (B  B) / 4

25. Basic Principles of Magnetohydrodynamic Jet Production (continued)
Typical results (e.g., Kudoh et al [1998]; Uchida et al. [1999])
Differential rotation twists up field into toroidal component, slowing rotation
Disk accretes inward, further enhancing differential rotation and B
Greatest field enhancement is at torus inner edge
Magnetic pressure gradient (dB2 / dZ) accelerates plasma out of system
Magnetic tension [hoop stress] (–B2/R) pinches and collimates the outflow into a jet
Outflow jet speed is of order the escape velocity from the inner edge of the torus (Vjet ~ VAlfven ~ Vesc)
Jet direction is along the rotation axis
Kudoh, Matsumoto, & Shibata (2002)

26. Simulated jet evolution in the ISM

27. The basic jet emission model for the flat-spectrum core
4/17/2017
The basic jet emission model for the flat-spectrum core
Blandford & Königl (1979), Falcke & Biermann (1995)
Plasma freely expanding in a supersonic jet
B r-1, n r-2, e ~ const
superposition of self-absorbed synchrotron spectra
at each frequency one sees the  = 1 surface as the “core”flat spectrum
subject to rel. boosting
Jets are messy - their radio cores are simple

28. The Spectrum of Jet-Cores: Free Expansion Approach
4/17/2017
The Spectrum of Jet-Cores: Free Expansion Approach
Plasma propagates at a constant proper speed  vz=jjc.
The (isothermal) plasma expands with sound speed  vr=ssc.
The resulting shape is a cone with Mach number vr vz 

29. The Spectrum of Jet-Cores: Particle and Energydensity Scaling
4/17/2017
The Spectrum of Jet-Cores: Particle and Energydensity Scaling
Particle conservation:
Energy conservation: vr vz 

30. The Spectrum of Jet-Cores: Synchrotron Absorption
4/17/2017
The Spectrum of Jet-Cores: Synchrotron Absorption
Synchrotron Absorption:
At a specific observing frequency we see the =1 surface; the location is frequency dependent:
r=1-1 vr vz 

31. The Spectrum of Jet-Cores: Synchrotron Emission
4/17/2017
The Spectrum of Jet-Cores: Synchrotron Emission
Synchrotron Emission:
The emission is dominated by the =1 surface.
For a conical jet the spectrum is flat! vr vz 

32. Size and Spectrum of Sgr A* (Galactic Center)
“submm-bump”
size
10 g
100 Rg
1000 Rg
1 Rg
Size of Sgr A*
cut-off
event horizon
shadow of event horizon
Melia & Falcke (2001, Ann. Rev. Astron.&Astroph)
The spectrum cuts off at the size scale of the event horizon!

33. The Synchrotron Spectrum of Jets
4/17/2017
The Synchrotron Spectrum of Jets
Rmin
Mbh~108 
Mbh~10
Rmin
 max S
Opt/UV/X
Radio/mm
 max S
S~-0.7
Radio/mm 
In jets r-1  max  rmin-1 Mbh-1 Turnover Frequency in stellar black holes >> blazars!

34. Scaling of Jets: large, small, powerful and faint
Scaling laws for Blandford & Königl jet cores.
The basic shape of the broad-band jet spectrum is (relatively) invariant to changes in black hole mass and accretion rate.
Simple scaling laws with Mdot can be derived analytically.
Assumption MdotPjet!
Radio/optical/X-ray ratio depends on Mbh and Mdot!
Smaller black holes peak at higher frequencies.
Increasing Mdot increases flux density non-linearly.
black hole mass
Falcke & Biermann (1995) Markoff et al. (2003)
Falcke et al. (2003) see also: Heinz & Sunyaev (2003)
and Merloni et al. (2003)

35. Jet Model for the X-Ray Binary XTE J1118+480
4/17/2017
Jet Model for the X-Ray Binary XTE J
Markoff, Falcke, Fender (2001) .

36. The Power-Evolution of XRBs
4/17/2017
The Power-Evolution of XRBs
Radio & X-ray Spectrum
Accretion Disk
Radio Jet
-disk
ADAF
Thermal disk spectrum
Disk corona or jet spectrum?
-disk
ADAF
Non-thermal jet spectrum
 -disk
ADAF
Fender (2000)

37. Spectrum of a Luminous Quasar
thermal (disk)
inverse Compton (jet)
Synchrotron (jet)
Lichti et al. (1994)

38. “JDAFs” Jet-Dominated Accretion Flows
The SED has jet and disk contributions!
At lower accretion rates disks become less and less prominent, jets remain strong.
Sub-Eddington black hole SEDs may be jet-dominated.
Lx,r
jet domination – disk domination
Disk
Jet
low-state
high-state
(A/C)DAF + Jet
ADAF: Esin, Narayan et al. (1997 …) Körding, Falcke, & Markoff (2002); see also Fender, Gallo, & Jonker (2003)

39. Scaling of Jets: large, small, powerful and faint
Scaling laws for Blandford & Königl jet cores.
Remember in the jet model: Radio/optical/X-ray ratio depends on Mbh and Mdot!
Assuming that the scaling-laws are correct, radio, optical, mass, and accretion rate are connected: .
E.g. one predicts that all jet-dominated BHs lie on a plane in the parameter space given by mass, accretion rate, and X-ray emission
This means: if one simply plots radio vs. X-ray emission of BHs the data will be scattered (since there is a range in mass and accretion rate), however, if one scales the X-ray emission to a common mass, there will be more order in the chaos…
black hole mass
Falcke & Biermann (1995) Markoff et al. (2003)
Falcke et al. (2003) see also: Heinz & Sunyaev (2003)
and Merloni et al. (2003)

40. Fundamental Plane: Radio, X-Rays, and Mass
Stellar mass BHs
Supermassive BHs
Mass corrected
Corrected for mass
Merloni, Heinz, Matteo (2003)
Falcke, Körding, Markoff (2004)

41. Restriction to Sub-Eddington BHs: XRBs, LLAGN, FRIs, BL Lacs
Sample containing only Low-State AGNs
FRIs & BL Lacs
jet-scaling
LLAGN (LINERS)
X-ray emission Scaled to common mass
XRBs
Testing different scaling laws
=0.4 dex
jet-disk scaling
Radio emission
Falcke, Körding, Markoff (2004) Körding, Falcke, Corbel (2005)

42. Power Unification Black holes have no hair!
Stellar and supermassive blacks have more and more in come …
BH, Jet, disk, variability
Main parameters: M,Mdot
XRB state transitions seem to have their equivalent in AGN classes
Sub-Eddington Black Holes may turn from disk- to jet-dominated.
Spectrum dominated by jet
Energy output dominated by (kinetic) jet power
Fundamental plane of BH activity describes spectral evolution (best for sub-Eddington BHs)
Radio quietness related to jet-quenching in High-state or not?
Falcke, Körding, Markoff (2004)

43. Feedback in radio-loud AGN?
Feedback of radio-loud AGN
into the surrounding IGM
(seen through X-ray here).
The kinetic impact of jets causes the X-ray gas to be displaced.
The consequence are holes in the X-ray emission.
Fabian et al.

44. Black Hole powered jet in M87
4/17/2017
Black Hole powered jet in M87
M87 is considered a low-luminosity AGN.
Radio jet powers huge radio lobe and pushes out hot X-ray gas.
Energy output from black hole dominates environment of galaxy.
260,000 Light years
16,000 Light years
VLA 327 MHz: Owen et al. (1999)

45. Radio Loud AGN: FR I – FR II
Weak or no emission lines, no blue bump
Strong emission lines,
blue bumps seen
Radio Power

46. FR I/FR II division Owen-Ledlow diagram
FRI and FRII radio galaxies delineated by sharp division in optical/ radio luminosity plane
Bigger galaxies need more powerful radio galaxies for the jets to emerge unharmed by shear forces in the ISM.
FR II
FR I
Owen & Ledlow (last century)

47. Shock waves in jets Lifetimes short compared to extent of jets
=> additional acceleration required.
Most jet energy is ordered kinetic energy.
Gas flow in jet is supersonic; near hot spot gas decelerates suddenly
=> shock wave forms. Energy now in relativistic
e- and mag field.

48. Particle Acceleration in jets: shocks and more
M87 jet spectra of bright knots
Emission is typically in power law form
Meisenheimer et al. (1997)
Optical and perhaps X-ray synchrotron require TeV electrons and continuous re-acceleration in the jet!

49. Radio Spectra: Age Effects
1. Energy loss
2. Self-absorption in the relativistic electrons gas
3. Absorption from ionized gas between us
and the source (free-free absorption) -> torus!
Reality
Theory
cooling
absorption

50. Electron Energy Distribution in Jets
dNe(ge) dge
dNe(ge) dge
The typical energy distri-bution of relativistic electrons is a power-law in ge (E=gemec2).
 ge-2
dNe(ge) dge Sn
nBge2
The energy of electrons is related to a characteristic frequency.
A power-law in the ener-gy distribution produces a powerlaw in the spectrum ge
n0.5 1
100
104

51. Electron Energy Distribution in JetsSn
Coincidentally in the inner jet region the low-frequency spectrum is self-absorbed.
nBge2
Hence, electrons with 1  ge 100 remain invisble but they could make up 99% of the total electron content!
 ge-2
dNe(ge) dge ge
Ntotgmin -1
n0.5 1
100
104

52. Energy loss
The relativistic electrons can loose energy because of a number of process
(adiabatic expansion of the source, synchrotron emission, inverse-Compton etc.).
the characteristics of the radio source and in particular the energy distribution N(E)
(and therefore the spectrum of the emitted radiation) tend to modify with time.
Adiabatic expansion: strong decrease in luminosity but the spectrum is unchanged
Energy loss through radiation:
After a time tb only the particle with E0<E* still survive while those with E0>E* have lost
their energy.
For ν < νbreak the spectral index remains constant (α = α0)
For ν > νbreak
νbreak ~ B-3 tyr-2
Single burst
α = (α0-1/2)‏
Continuous injection

53. Energy loss Typical spectral index of the lobes   = 0.7
These energy lost affect mainly the large scale structures (e.g. lobes).
Typical spectral index of the lobes   = 0.7
Typically Myr for B=10μG, freq 8-1 GHz
Unless there is re-acceleration in some regions of the radio source!

54. Self-absorption in the relativistic electron gas
Optically thick case: the internal absorption from the electrons needs to be considered the brightness temperature of the source is close to the kinetics temperature of the electrons.
The opacity is larger at lower frequency -> plasma opaque at low frequencies and transparent at high
Frequency corresponding to =1

55. Self-absorption in the relativistic electron gas
Affects mainly the central
compact region or very small
radio sources
Higher “turnover” frequency
smaller size of the
emitting region.

56. Gigahertz Peak Spectrum and Compact Steep Spectrum Sources
GPS = Gigahertz Peak Spectrum – characterized by a peak in the radio spectrum at ~ 1 GHz
CSS = Compact Steep Spectrum – have steep spectra at microwave frequencies but also have a peak in the spectrum in the MHz range

57. GPS & CSS Sources – young (and frustrated sources)
GPS (GHz-Peaked-Spectrum) and CSS (Compact-Steep-Spectrum) sources are young radio jets that are still stuck in the dense ISM.
GPS
D=68 Mpc
5pc/mas
Size: ~250 pc
CSS
Turn-over frequency scales inversely with size
Likely effect of self-absorption.
O’Dea 1998

58. GPS at work: The “Seyfert” Galaxy III Zw 2
Flux increase by factor within years
Outbursts roughly every 5 years
Radio monitoring campaign set up in anticipation of current outburst
Aller et al., priv. com.

59. The Extreme Variability of the Seyfert Galaxy III Zw 2
Flux increase by factor 40 (!) within 2 years
Outburst peaks at 7mm
Textbook-like self-absorbed spectrum (a=2-2.5)
Fitted by two synchro-tron components.
Millimeter-Peaked-Spectrum(MPS) l=7mm
Falcke, Bower, et al. (1999, ApJL)

60. III Zw 2 - Spectral Evolution
The spectrum remained highly inverted, peaking at 43 GHz during the rise of the outburst.
Peak frequency dropped quickly after peak in 43 GHz lightcurve (decay).
Rise
Rise
Decay
Decay

61. III Zw 2 - Structural Evolution
The source remained ultra-compact during the rise, but requiring at least two compo-nents separated by 72mas (=0.1 pc).
No other components found!
Structural expansion seen during the decay.
Rise
Decay

62. Evolution of III Zw 2 Simultaneous VLBI and VLA observations
Very close corres- pondence between spectral and struc- tural evolution!
VLBI monitoring
superresolved (150mas)
5 epochs interpolated
VLA monitoring
Monthly sampling
13 epochs interpolated
Brunthaler, Falcke, Bower et al. (2000)

63. Polarization
Characteristic of the synchrotron emission: the radiation is highly polarized.
For an uniform magnetic field, the polarization of an ensemble of electrons is linear, perpendicular to the magnetic field and the fractional polarization is given by:
for 2<p<4
never!
Typical polarization from few to ~20%
Tangled magnetic field

64. Polarization Polarization between 10 and 20%
(some peaks at ~40% around the edge of the lobes)‏

65. Polarization
Example of polarization in radio jets.

66. Faraday rotation at different wavelengths
Travel through a plasma+magnetic field (that can be internal or external to the source) changes the polarization angle
Ne = electron density of the plasma
dl = depth
B = component of the magnetic field
parallel to line of sight
Rotation measure (RM)‏
RM can be derived via observations
at different wavelengths
If the medium is in front of the radio source: no change in the fractional polarization
If the medium is mix in the radio source: depolarization dependence on wavelength (if due to Faraday rotation)‏
thermal electrons with density ~ 10-5 cm-3
Depolarization happens also if the magnetic field is tangled on the scale of the
beam of the observations

67. Different types of radio galaxies
The morphology of a radio galaxy may depend on
different parameters:
- radio power (related to the power of the AGN?)‏
- orientation of the radio emission
- intrinsic differences in the
(nuclear regions of) host galaxy
- environment

68. Different types of radio galaxies

69. Different types of radio galaxies
~200 kpc
The morphology
does not depend
on size!
~20 pc

70. Effects of the interaction
with the environment
Effects of age

71. Restarting Jets
V.L. Safouris, G.V. Bicknell, R.S. Sunrahmanyan & L. Saripalli, 2006, ApJ

72. Summary
Jets are ubiquitous and are seen in almost all types of sources at all black hole masses and all accretion rates.
They are hot, collimated plasma streams close to the speed of light, beaming plays a role
They are launched close to the black hole.
They can carry a few percent of the total accretion power in the form of kinetic energy.
Emission ranges over the entire e.m. spectrum – main processes are synchrotron and inverse Compton emission.